Sulfide-based solid electrolyte, method for producing the sulfide-based solid electrolyte, and method for producing all-solid-state battery

ABSTRACT

Provided is a method for producing a sulfide-based solid electrolyte with a balance between the ion conductivity of the sulfide-based solid electrolyte and the heat generation amount of an electrode layer containing the sulfide-based solid electrolyte during an electrode reaction. Disclosed is a method for producing a sulfide-based solid electrolyte comprising a sulfide glass-based material that contains at least one lithium halide compound selected from the group consisting of LiI, LiBr and LiCl, the method comprising immersing the sulfide glass-based material, which is at least one sulfide glass-based material selected from the group consisting of a sulfide glass and a glass ceramic, in an organic solvent having a solubility parameter of  7.0  or more and  8.8  or less, for  1  hour to  100  hours.

CROSS-REFERENCE

This is a continuation of Application No.: 16/403,779 filed May 6, 2019,claiming priority from Japanese Patent Application No. 2018-096514 filedMay 18, 2018, which is incorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to a sulfide-based solid electrolyte, a methodfor producing the sulfide-based solid electrolyte, and a method forproducing an all-solid-state battery.

BACKGROUND ART

In recent years, with the rapid spread of IT and communication devicessuch as personal computers, camcorders and cellular phones, greatimportance has been attached to the develo μment of batteries that canbe used as the power source of such devices. In the automobile industry,etc., high-power and high-capacity batteries for electric vehicles andhybrid vehicles are under develo μment.

Of all-solid-state batteries, an all-solid-state lithium ion secondarybattery has attracted attention, due to its high energy densityresulting from the use of a battery reaction accompanied by lithium iontransfer, and due to the use of a solid electrolyte as the electrolytepresent between the cathode and the anode, in place of a liquidelectrolyte containing an organic solvent. Also, various studies havebeen conducted on sulfide-based solid electrolyte as the solidelectrolyte.

In Patent Literature 1, it is disclosed to produce a sulfide-basedall-solid-state battery by use of an alkali metal sulfide having aspecific surface area of 10.0 m²/g, which is a specific surface areameasured by the BET method.

Patent Literature 2 discloses a sulfide-based all-solid-state battery inwhich a cathode active material layer contains, with respect to itsmass, 0.078 mass % to 0.330 mass % of butyl butyrate.

CITATION LIST

Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No.2014-212065

Patent Literature 2: JP-A No. 2016-134302

SUMMARY OF INVENTION Technical Problem

In an all-solid-state battery comprising an electrode of conventionalelectrode structure, a heat generation reaction occurs on a contactsurface between a solid electrolyte and an active material. Therefore,there is a problem of large heat generation and low electrode thermalstability.

A sulfide-based solid electrolyte used in an electrode material isrequired to have high ion conductivity.

In light of the above circumstance, an object of the disclosedembodiments is to provide a sulfide-based solid electrolyte with abalance between the ion conductivity of the sulfide-based solidelectrolyte and the heat generation amount of an electrode layercontaining the sulfide-based solid electrolyte during an electrodereaction, a method for producing the sulfide-based solid electrolyte,and a method for producing an all-solid-state battery.

Solution to Problem

In a first embodiment, there is provided a method for producing asulfide-based solid electrolyte comprising a sulfide glass-basedmaterial that contains at least one lithium halide compound selectedfrom the group consisting of LiI, LiBr and LiCl, the method comprisingimmersing the sulfide glass-based material, which is at least onesulfide glass-based material selected from the group consisting of asulfide glass and a glass ceramic, in an organic solvent having asolubility parameter of 7.0 or more and 8.8 or less, for 1 hour to 100hours.

The organic solvent may be butyl butyrate.

When the sulfide glass-based material is a sulfide glass, the method forproducing the sulfide-based solid electrolyte may further compriseheating the sulfide glass at a temperature higher than a crystallizationtemperature (Tc) of the sulfide glass, which is a temperature observedby thermal analysis measurement, thereby obtaining a glass ceramic.

In another embodiment, there is provided a method for producing anall-solid-state battery comprising a cathode layer that contains thesulfide-based solid electrolyte obtained by the above-mentionedproduction method.

In another embodiment, there is provided a sulfide-based solidelectrolyte comprising a sulfide glass-based material that contains atleast one lithium halide compound selected from the group consisting ofLiI, LiBr and LiCl, wherein a specific surface area of the sulfide-basedsolid electrolyte measured by the BET method, is from 10 m²/g to 35m²/g.

Advantageous Effects of Invention

According to the disclosed embodiments, a sulfide-based solidelectrolyte with a balance between the ion conductivity of thesulfide-based solid electrolyte and the heat generation amount of anelectrode layer containing the sulfide-based solid electrolyte during anelectrode reaction, a method for producing the sulfide-based solidelectrolyte, and a method for producing an all-solid-state battery, canbe provided.

BRIEF DESCRIPTION OF DRAWING

In the accompanying drawing,

FIG. 1 is a schematic view of an all-solid-state battery obtained by theproduction method of the disclosed embodiments.

DESCRIPTION OF EMBODIMENTS 1. Method for Producing Sulfide-Based SolidElectrolyte

The sulfide-based solid electrolyte production method according to thedisclosed embodiments, is a method for producing a sulfide-based solidelectrolyte comprising a sulfide glass-based material that contains atleast one lithium halide compound selected from the group consisting ofLiI, LiBr and LiCl, the method comprising immersing the sulfideglass-based material, which is at least one sulfide glass-based materialselected from the group consisting of a sulfide glass and a glassceramic, in an organic solvent having a solubility parameter of 7.0 ormore and 8.8 or less, for 1 hour to 100 hours.

A problem with all-solid-state batteries is that heat generation occursin an electrode material and causes a reduction in the thermal stabilityof the electrode.

It was found that even when a heat generation reaction occurs on acontact surface between a sulfide-based solid electrolyte and an activematerial, an increase in the heat generation amount of the wholeelectrode is suppressed as long as the sulfide-based solid electrolytehas a desired porosity and a desired crystallinity.

In particular, by forming a sulfide-based solid electrolyte into a glassceramic, the ion conductivity and crystallinity of the sulfide-basedsolid electrolyte are increased. Moreover, by forming the sulfide-basedsolid electrolyte into a porous solid electrolyte, the heat dissipatingperformance of the sulfide-based solid electrolyte is increased.Finally, by using the sulfide-based solid electrolyte in an electrodelayer, the thermal stability of the electrode layer can be increased.

In addition, by lengthening the time for immersion of the sulfide-basedsolid electrolyte in an organic solvent, the BET specific surface areaof the sulfide-based solid electrolyte is increased to increase theporosity, and the heat generation amount of the electrode layercontaining the sulfide-based solid electrolyte is further decreased.

The sulfide-based solid electrolyte according to the disclosedembodiments comprises a sulfide glass-based material that contains atleast one lithium halide compound selected from the group consisting ofLiI, LiBr and LiCl.

The type of elements contained in the sulfide glass-based material, canbe confirmed by an inductively coupled plasma atomic emissionspectrometer, for example.

As the sulfide glass-based material, examples include, but are notlimited to, a sulfide glass and a glass ceramic. From the viewpoint ofincreasing ion conductivity, the sulfide glass-based material may be aglass ceramic.

In the disclosed embodiments, the glass ceramic is a material obtainedby crystallizing a sulfide glass. For example, by an X-ray diffractionmethod, it is possible to check whether the sulfide glass-based materialis a glass ceramic or not.

In the disclosed embodiments, a sulfide glass-based material having acrystallinity of from 60% to 80%, which is measured by an X-raydiffraction method, is referred to as the glass ceramic.

Also in the disclosed embodiments, the sulfide glass refers to amaterial synthesized by amorphizing a raw material composition. Thesulfide glass means not only “glass” in a strict sense, for whichcrystal periodicity is not observed by X-ray diffraction measurement orthe like, but also materials in a general sense, which are synthesizedby amorphization by the below-described mechanical milling. Accordingly,even when a material is observed by X-ray diffraction measurement or thelike and a peak derived from a raw material (such as LiI) is observed,the material corresponds to a sulfide glass as long as it is a materialsynthesized by amorphization.

The ion conductivity of a glass ceramic is higher than that of a sulfideglass, for example. Therefore, an all-solid-state battery comprising aglass ceramic can obtain lower internal resistance than anall-solid-state battery comprising a sulfide glass.

The sulfide-based solid electrolyte according to the disclosedembodiments may contain at least one sulfide glass-based materialselected from the group consisting of a sulfide glass and a glassceramic. From the viewpoint of increasing ion conductivity, thesulfide-based solid electrolyte may contain a glass ceramic.

The sulfide-based solid electrolyte according to the disclosedembodiments may contain at least the sulfide glass-based material. Thesulfide-based solid electrolyte may be composed of only the sulfideglass-based material.

The raw material composition of the sulfide-based solid electrolyte ofthe disclosed embodiments, contains a Li element, an S element, and atleast one halogen element selected from the group consisting of I, Brand Cl. As needed, it further contains at least one selected from thegroup consisting of a P element, an O element and an S element.

As the raw material composition, examples include, but are not limitedto, a material having the composition of a(LiX)·(1-a) (bLi₂S·(1-b)P₂S₅)(where X is at least one halogen element selected from the groupconsisting of I, Br and Cl; “a” corresponds to the total proportion ofLiX; and “b” corresponds to the proportion of Li₂S).

As the raw material composition, examples include, but are not limitedto, LiI-Li₂S-SiS₂, LiI-Li₂S-P₂S₅, LiI-Li₂S-P₂O₅, LiI-Li₃PO₄-P₂S₅,LiI-Li₂O-Li₂S-P₂S₅, and LiBr-LiI-Li₂S-P₂S₅.

More specifically, examples include, but are not limited to,15LiBr·10LiI·75(0.75Li₂S·0.25P₂S₅) and 70 (0.06Li₂O·0.69Li₂S·0.25P₂S₅)·30LiI. These compositions are on a molar basis.

As the method for amorphizing the raw material composition, examplesinclude, but are not limited to, mechanical milling and a melt-quenchingmethod. The method may be mechanical milling. This is because the rawmaterial composition can be amorphized at normal temperature, and theproduction process can be simplified.

The melt-quenching method has a limit to a reaction atmosphere orreaction container used. Meanwhile, the mechanical milling isadvantageous in that a sulfide glass having a desired composition can besimply and easily synthesized.

The mechanical milling may be dry or wet mechanical milling. Themechanical milling may be the latter. This is because the raw materialcomposition can be prevented from attaching to the inner wall surface ofa container, etc., and a sulfide glass with higher amorphous nature canbe obtained.

The mechanical milling is not particularly limited, as long as it is amethod for mixing the raw material composition by applying mechanicalenergy thereto. The mechanical milling may be carried out by, forexample, a ball mill, a vibrating mill, a turbo mill, mechanofusion, ora disk mill. The mechanical milling may be carried out by a ball mill,or it may be carried out by a planetary ball mill. This is because thedesired sulfide glass can be efficiently obtained.

The conditions of the mechanical milling are determined so that thedesired sulfide glass can be obtained. For example, in the case of usingthe planetary ball mill, the raw material composition and grinding ballsare put in a container, and mechanical milling is carried out at apredetermined rotational frequency for a predetermined time. In general,the larger the rotational frequency, the faster the production speed ofthe sulfide glass, and the longer the treatment time, the higher theconversion rate of the raw material composition into the sulfide glass.

In the case of using the planetary ball mill, the plate rotationalfrequency is in a range of from 200 r μm to 500 r μm, for example. Theplate rotational frequency may be in a range of 250 r μm to 400 r μm.

In the case of using the planetary ball mill, the mechanical millingtime is in a range of from 1 hour to 100 hours, for example. Themechanical milling time may be in a range of from 1 hour to 50 hours.

As the material of the container and grinding balls used in the ballmill, examples include, but are not limited to, ZrO₂ and Al₂O₃.

The diameter of the grinding balls is in a range of from 1 mm to 20 mm,for example.

A liquid is used for wet mechanical milling. The liquid may be a liquidthat does not produce hydrogen sulfide in a reaction with the rawmaterial composition. Hydrogen sulfide is produced when protons aredissociated from the molecules of the liquid and reacted with the rawmaterial composition or sulfide glass. Therefore, the liquid may haveaprotic properties to a degree that does not result in the production ofhydrogen sulfide. Aprotic liquids can be broadly classified into polarand non-polar aprotic liquids.

The polar aprotic liquid is not particularly limited. As the polaraprotic liquid, examples include, but are not limited to, ketones suchas acetone; nitriles such as acetonitrile; amides such asN,N-dimethylformamide (DMF); and sulfoxides such as dimethylsulfoxide(DMSO).

As the non-polar aprotic liquid, examples include, but are not limitedto, aromatic hydrocarbons such as benzene, toluene and xylene; chainethers such as diethyl ether and dimethyl ether; cyclic ethers such astetrahydrofuran; alkyl halides such as chloroform, methyl chloride andmethylene chloride; esters such as ethyl acetate; and fluorine compoundssuch as benzene fluoride, heptane fluoride, 2,3-dihydroperfluoropentane,and 1,1,2,2,3,3,4-heptafluorocyclopentane. The amount of the addedliquid is not particularly limited, and it may be an amount to a degreethat can obtain the desired sulfide-based solid electrolyte.

The method for producing the sulfide-based solid electrolyte accordingto the disclosed embodiments comprises at least (1) immersing. Asneeded, it further comprises (2) heating.

Hereinafter, the immersing and heating will be described in order.

(1) Immersing

The immersing is immersing the sulfide glass-based material, which is atleast one of a sulfide glass and a glass ceramic, in an organic solventhaving a solubility parameter of 7.0 or more and 8.8 or less, for 1 hourto 100 hours.

By immersing the sulfide glass-based material in the organic solvent,impurities, glass components, unreacted raw materials, etc., on thesurface and in the pores of the sulfide glass-based material can beeluted into the organic solvent and removed. Therefore, the surface ofthe sulfide glass-based material and the inside of the pores of thesulfide glass-based material are roughened, and desired pores can beformed in the sulfide glass-based material.

As a result, it is presumed that the sulfide-based solid electrolytehaving the desired porosity is formed, and the chemical stability of thesulfide-based solid electrolyte can be increased.

Also, oxidation of an electrode layer comprising the sulfide-based solidelectrolyte is suppressed, and the durability of the electrode layer isincreased.

In the immersing, a glass ceramic having a crystallinity of from 60% to80% may be used as the sulfide glass-based material, because impurities,glass components, unreacted raw materials, etc., on the surface and inthe pores of the glass ceramic can be sufficiently eluted into theorganic solvent and removed. Meanwhile, when a crystal material having acrystallinity of more than 80% is used in the immersing, it is presumedthat impurities, glass components, unreacted raw materials, etc., on thesurface and in the pores of the crystal material cannot be sufficientlyeluted into the organic solvent, and the desired porosity cannot beobtained unlike the case of using the sulfide glass-based material.

The organic solvent is not particularly limited, as long as it has asolubility parameter of 7.0 or more and 8.8 or less.

The solubility parameter of the disclosed embodiments is the Hansensolubility parameter (HSP). The solubility parameter may be a value byreference to, for example, “Chemical Handbook: Advanced” (revised 3rdedition) published by Maruzen Publishing Co., Ltd, “Handbook ofAdhesion” (4th edition) published by Nikkan Kogyo Shimbun Ltd., or“Polymer Data Handbook” edited by The Society of Polymer Science, Japan.

As the organic solvent, examples include, but are not limited to, butylbutyrate (solubility parameter: 8.5), diethyl ether (solubilityparameter: 7.4), cyclohexane (solubility parameter: 8.2), toluene(solubility parameter: 8.8), chlorotoluene (solubility parameter: 8.8),hexyl acetate (solubility parameter: 7.2), n-pentane (solubilityparameter: 7.0) and n-octane (solubility parameter: 7.5). The organicsolvent may be butyl butyrate. The organic solvent may be one kind oforganic solvent, or it may be a mixed solvent obtained by mixing two ormore kinds of organic solvents. When the organic solvent has asolubility parameter of less than 7.0, it may be difficult to obtain thesulfide-based solid electrolyte having the desired porosity, even if thesulfide glass-based material is immersed therein. Also, a long period ofimmersion may be needed to obtain the sulfide-based solid electrolytehaving the desired porosity.

The amount of the organic solvent used is not particularly limited, aslong as it is an amount that allows the sulfide glass-based material tobe entirely immersed in the organic solvent.

For the immersing, the immersing time may be 1 hour to 100 hours.

The immersing temperature is not particularly limited. From theviewpoint of ease of handling, the lower limit of the immersingtemperature may be 10° C. or more. From the viewpoint of shortening theimmersing time, the upper limit may be a temperature less than theboiling point of the organic solvent. From the viewpoint of ease ofhandling, the upper limit may be 30° C. or less.

The immersing atmosphere may be an inert gas atmosphere such as Ar andN₂.

In the immersing, pressure is applied. The pressure is not particularlylimited, and it may be the atmospheric pressure.

The sulfide glass-based material to be immersed may be in a sulfideglass state or a glass ceramic state.

(2) Heating

The heating is heating the sulfide glass at a temperature higher than acrystallization temperature (Tc) of the sulfide glass, which is atemperature observed by thermal analysis measurement, thereby obtaininga glass ceramic.

By heating the sulfide glass, the crystallization point of thesulfide-based solid electrolyte is increased; therefore, thecrystallinity of the sulfide-based solid electrolyte is increased toincrease the ion conductivity of the sulfide-based solid electrolyte.

The crystallization temperature (Tc) of the sulfide glass can bemeasured by thermal analysis measurement (DTA).

For the heating, the heating temperature may be a temperature higherthan the crystallization temperature (Tc) of the sulfide glass, which isa temperature observed by thermal analysis measurement. In general, itis 195° C. or more. The heating temperature may be 200° C. or more, orit may be 205° C. or more. On the other hand, the upper limit of theheating temperature is not particularly limited.

The heating time is not particularly limited, as long as the desiredglass ceramic is obtained. For example, it is in a range of from oneminute to 24 hours, or it may be in a range of from one minute to 10hours.

The heating may be carried out in an inert gas atmosphere such as argongas and nitrogen gas, or it may be carried out in a reduced-pressureatmosphere (especially in a vacuum). This is because a deterioration(e.g., oxidation) of the sulfide-based solid electrolyte can beprevented.

The heating method is not particularly limited. For example, a methodusing a firing furnace may be used.

In the sulfide-based solid electrolyte obtained by the heating, thesulfide glass may be absolutely formed into a glass ceramic by theheating, or the sulfide glass may fail to be formed into a glass ceramicand may remain in the sulfide-based solid electrolyte. From theviewpoint of increasing ion conductivity, the sulfide glass may beabsolutely formed into a glass ceramic.

2. Sulfide-Based Solid Electrolyte

The sulfide-based solid electrolyte according to the disclosedembodiments, is a sulfide-based solid electrolyte comprising a sulfideglass-based material that contains at least one lithium halide compoundselected from the group consisting of LiI, LiBr and LiCl, wherein aspecific surface area of the sulfide-based solid electrolyte measured bythe BET method, is from 10 m²/g to 35 m²/g.

By using the sulfide-based solid electrolyte having a specific surfacearea of 10 m²/g or more as a material for the electrode layer, the heatdissipating performance of the sulfide-based solid electrolyte isincreased. Therefore, the heat generation amount of the electrode layercan be reduced to a desired value or less.

On the other hand, when the BET specific surface area is more than 35m²/g, the ion conductivity of the sulfide-based solid electrolyte isdecreased to less than the desired value, and the performance of theelectrode layer is decreased.

Therefore, as long as the BET specific surface area is from 10 m²/g to35 m²/g, the sulfide-based solid electrolyte obtains a balance betweenthe ion conductivity of the sulfide-based solid electrolyte and the heatgeneration amount of the electrode layer containing the sulfide-basedsolid electrolyte during an electrode reaction.

For the specific surface area of the sulfide-based solid electrolytemeasured by the BET method, the lower limit is 10 m²/g or more, or itmay be more than 10 m²/g or may be 12.7 m²/g or more. The upper limit is35 m²/g or less, or it may be less than 35 m²/g or may be 33.4 m²/g orless. In the disclosed embodiments, the BET specific surface area isused as an index of the porosity of the sulfide-based solid electrolyte.

The BET specific surface area of the sulfide-based solid electrolyte canbe increased by immersing the sulfide-based solid electrolyte in anorganic solvent. The type of the organic solvent and the immersing timewill not be described here, since they are the same as those describedabove under “1. Method for producing sulfide-based solid electrolyte”.

The sulfide glass-based material contained in the sulfide-based solidelectrolyte will not be described here, since it is the same as thesulfide glass-based material described above under “1. Method forproducing sulfide-based solid electrolyte”.

The sulfide-based solid electrolyte of the disclosed embodiments maycontain at least the sulfide glass-based material, or it may be composedof only the sulfide glass-based material.

For the lithium ion conductivity of the sulfide-based solid electrolyteof the disclosed embodiments at normal temperature, the lower limit is2.0 mS/cm or more, or it may be 2.7 mS/cm or more. The upper limit isnot particularly limited and may be 3.9 mS/cm or less.

The crystallinity of the sulfide-based solid electrolyte is notparticularly limited. From the viewpoint of increasing ion conductivity,the lower limit is 60% or more, or it may be 69% or more. The upperlimit is 80% or less, or it may be 75% or less.

The crystallinity can be measured by an X-ray diffraction method or thelike.

The heat generation amount of the electrode layer of the sulfide-basedsolid electrolyte of the disclosed embodiments, may be as small aspossible. From the viewpoint of balance with ion conductivity, the heatgeneration amount may be from 477 W/g to 753 W/g. The heat generationamount can be measured by use of a differential scanning calorimeter(DSC) or the like.

As the form of the sulfide-based solid electrolyte of the disclosedembodiments, examples include, but are not limited to, a particle form.The average particle diameter (D₅₀) of the sulfide-based solidelectrolyte in the particle form may be in a range of from 0.1 μm to 50μm.

In the disclosed embodiments, the average particle diameter of particlesis a value measured by laser diffraction/scattering particle sizedistribution measurement. Also in the disclosed embodiments, the mediandiameter (D₅₀) of particles is a diameter at which, when the particlediameters of the particles are arranged in ascending order, theaccumulated volume of the particles is half (50%) the total number ofthe particles.

The sulfide-based solid electrolyte of the disclosed embodiments can beused in any desired intended application that needs Li ion conductivity.The sulfide-based solid electrolyte may be used in a battery.

Also, the present disclosure can provide a method for producing anall-solid-state battery comprising the above-described sulfide-basedsolid electrolyte. The sulfide-based solid electrolyte may be used in acathode layer, an anode layer, or a solid electrolyte layer. Thesulfide-based solid electrolyte may be used in a cathode layer.

3. Method for Producing All-Solid-State Battery

The all-solid-state battery production method according to the disclosedembodiments, is a method for producing an all-solid-state batterycomprising a cathode layer that contains the sulfide-based solidelectrolyte obtained by the above-mentioned production method.

The method for producing the all-solid-state battery of the disclosedembodiments, is not particularly limited, except that the sulfide-basedsolid electrolyte obtained by the above-described production method, isincorporated in the cathode layer. The all-solid-state battery can beproduced by a conventionally known method.

For example, a solid electrolyte layer is formed by pressing a powder ofa solid electrolyte material containing a solid electrolyte. On onesurface of the solid electrolyte layer, an anode layer is formed bypressing a powder of a material for anode. Then, on the other surface ofthe solid electrolyte layer, which is a surface opposite to the surfaceon which the anode layer was formed, a cathode layer is formed bypressing a powder of a material for cathode, the material containing thesulfide-based solid electrolyte obtained by the above-mentionedproduction method. The thus-obtained cathode layer-solid electrolytelayer-anode layer assembly can be used as the all-solid-state battery.

In this case, press pressure is applied to press the powder of the solidelectrolyte material, the powder of the material for anode, and thepowder of the material for cathode. The press pressure is generallyabout 1 MPa or more and about 600 MPa or less.

The pressing method is not particularly limited. As the pressing method,examples include, but are not limited to, a method of applying the presspressure by use of a plate press machine, a roll press machine or thelike.

FIG. 1 is a schematic sectional view of an example of theall-solid-state battery obtained by the production method of thedisclosed embodiments.

As shown in FIG. 1, an all-solid-state battery 100 comprises a cathode16, an anode 17 and a solid electrolyte layer 11, the cathode 16including a cathode layer 12 and a cathode current collector 14, theanode 17 including an anode layer 13 and an anode current collector 15,and the solid electrolyte layer 11 being disposed between the cathode 16and the anode 17.

The cathode comprises at least a cathode layer. As needed, it furthercomprises a cathode current collector.

The cathode layer contains at least a cathode active material and, as asolid electrolyte, the sulfide-based solid electrolyte obtained by theabove-mentioned production method. As needed, it further contains anelectroconductive material and a binder.

As the cathode active material, a conventionally known material can beused. When the all-solid-state battery is a lithium battery, forexample, an elemental lithium metal, a lithium alloy or alithium-containing metal oxide can be used as the cathode activematerial. As the lithium alloy, examples include, but are not limitedto, an In-Li alloy. As the lithium-containing metal oxide, examplesinclude, but are not limited to, layered rock salt-type active materialssuch as LiCoO₂, LiNiO₂, LiVO₂ and LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂,spinel-type active materials such as LiMn₂O₄ and Li(Ni_(0.5)Mn_(1.5))O₄,and olivine-type active materials such as LiFePO₄, LiMnPO₄, LiNiPO₄ andLiCoPO₄.

The form of the cathode active material is not particularly limited. Asthe form, examples include, but are not limited to, a particle form anda plate form.

The content of the cathode active material in the cathode layer is notparticularly limited. For example, when the total volume of the cathodelayer is determined as 100 vol %, it may be from 50 vol % to 100 vol %.

As the solid electrolyte used in the cathode layer, the same solidelectrolyte as the solid electrolyte used in the below-described solidelectrolyte layer, may be further used, as long as at least thesulfide-based solid electrolyte obtained by the above-mentionedproduction method is used.

The content of the solid electrolyte in the cathode layer is notparticularly limited. For example, when the total volume of the cathodelayer is determined as 100 vol %, it may be from 10 vol % to 50 vol %.

As the electroconductive material, examples include, but are not limitedto, carbonaceous materials such as acetylene black and Ketjen black,fibrous carbon such as carbon fiber, and metal materials.

The content of the electroconductive material in the cathode layer isnot particularly limited. For example, when the total volume of thecathode layer is determined as 100 vol %, it may be from 0 vol % to 10vol %.

The binder is not particularly limited. As the binder, examples include,but are not limited to, butadiene rubber (BR), polyvinylidene fluoride(PVdF) and styrene-butadiene rubber (SBR).

The content of the binder in the cathode layer is not particularlylimited. For example, when the total volume of the cathode layer isdetermined as 100 vol %, it may be from 0 vol % to 10 vol %.

The thickness of the cathode layer is not particularly limited. Forexample, the thickness may be from 10 μm to 250 μm, or it may be from 20μm to 200 μm.

The method for forming the cathode layer is not particularly limited. Asthe method, examples include, but are not limited to, a method forforming the cathode layer by pressing the powder of the material forcathode, the material containing the cathode active material, thesulfide-based solid electrolyte obtained by the above-mentionedproduction method and, as needed, other components.

The cathode current collector functions to collect current from thecathode layer.

As the material for the cathode current collector, examples include, butare not limited to, metal materials such as SUS, Ni, Cr, Au, Pt, Al, Fe,Ti, Zn and Cu.

As the form of the cathode current collector, examples include, but arenot limited to, a foil form, a plate form and a mesh form.

The cathode may further comprise a cathode lead connected to the cathodecurrent collector.

The anode comprises at least an anode layer. As needed, it furthercomprises an anode current collector.

The anode layer contains at least an anode active material. As needed,it further contains a solid electrolyte, an electroconductive materialand a binder.

As the anode active material, a conventionally known material can beused. As the anode active material, examples include, but are notlimited to, Li metal, graphite, Si, Si alloy and Li₄Ti₅O₁₂ (LTO) .

As the Si alloy, examples include, but are not limited to, an alloy witha metal such as Li, and an alloy with at least one kind of metalselected from the group consisting of Sn, Ge and Al.

After the all-solid-state battery is assembled, initial charging of theall-solid-state battery is carried out. By the initial charging, Si isreacted with a metal such as Li to form an amorphous alloy. The alloyedpart remains amorphous even after metal ions such as lithium ions arereleased by discharging. In the disclosed embodiments, therefore, theanode layer comprising Si includes Si formed into an amorphous alloy.

The form of the anode active material is not particularly limited. Asthe form, examples include, but are not limited to, a particle form anda plate form.

The average particle diameter (the median diameter D₅₀ of the volumedistribution) of the anode active material particles may be 10 μm orless.

The content of the anode active material in the anode layer is notparticularly limited. For example, when the total volume of the anodelayer is determined as 100 vol %, it may be from 20 vol % to 100 vol %.

The solid electrolyte used in the anode layer may be the same as thesolid electrolyte used in the below-described solid electrolyte layer.

The content of the solid electrolyte in the anode layer is notparticularly limited. For example, when the total volume of the anodelayer is determined as 100 vol %, it may be from 0 vol % to 80 vol %.

The electroconductive material and binder used in the anode layer may bethe same as those used in the cathode layer.

The content of the electroconductive material in the anode layer is notparticularly limited. For example, when the total volume of the anodelayer is determined as 100 vol %, it may be from 0 vol % to 10 vol %.

The content of the binder in the anode layer is not particularlylimited. For example, when the total volume of the anode layer isdetermined as 100 vol %, it may be from 0 vol % to 10 vol %.

The thickness of the anode layer is not particularly limited. Forexample, the thickness may be from 10 μm to 100 μm. The thickness may befrom 10 μm to 50 μm.

The method for forming the anode layer is not particularly limited. Asthe method, examples include, but are not limited to, a method forforming the anode layer by pressing the powder of the material foranode, the material containing the anode active material and, as needed,other components.

The anode current collector functions to collect current from the anodelayer.

As the material for the anode current collector, the same material asthe material for the cathode current collector may be used.

As the form of the anode current collector, the same form as the form ofthe cathode current collector may be used.

The anode may further comprise an anode lead connected to the anodecurrent collector.

The solid electrolyte layer contains at least a solid electrolyte. Asneeded, it may further contain a binder, etc.

As the solid electrolyte used in the solid electrolyte layer, examplesinclude, but are not limited to, an oxide-based solid electrolytematerial and a sulfide-based solid electrolyte material.

As the sulfide-based solid electrolyte material, the sulfide-based solidelectrolyte obtained by the production method of the disclosedembodiments may be used, or a different material may be used. As thesulfide-based solid electrolyte material, examples include, but are notlimited to, Li₂S-SiS₂, LiI-Li₂S-SiS₂, LiI-Li₂S-P₂S₅, LiI-Li₂S-P₂₀₅,LiI-Li₃PO₄-P₂S₅, LiI-Li₂O-Li₂S-P₂S₅, LiBr-LiI-Li₂S-P₂S₅, andLi₂S-P₂S_(5.)

More specifically, examples include, but are not limited to, Li₇P₃S₁₁,Li₃PS₄, Li₈P₂S₉, Li₁₃GeP₃S₁₆, Li₁₀GeP₂S₁₂,15LiBr·10LiI·75(0.75Li₂S·0.25P₂S₀ and70(0.06Li₂O·0.69Li₂S·0.25P₂S₅)·30LiI. These compositions are on a molarbasis.

As the oxide-based solid electrolyte material, examples include, but arenot limited to, Li_(6.25)La₃Zr₂Al_(0.25)O₁₂, Li₃PO₄ andLi_(3+x)PO_(4-x)N_(x) (LiPON).

As the solid electrolyte, one kind of solid electrolyte may be usedalone, or two or more kinds of solid electrolytes may be used. In thecase of using two or more kinds of solid electrolytes, they may be mixedtogether, or each solid electrolyte may be formed into a layer, therebyobtaining a multilayered structure.

The solid electrolyte may be any one of a glass, a glass ceramic havinga crystallinity of from 60% to 80%, and a crystal material having acrystallinity of more than 80%. From the viewpoint of increasing lithiumion conductivity, the solid electrolyte may be a glass ceramic.

The form of the solid electrolyte is not particularly limited. As theform, examples include, but are not limited to, a particle form and aplate form. The solid electrolyte may be in a particle form.

The proportion of the solid electrolyte in the solid electrolyte layeris not particularly limited. For example, the proportion may be 50 mass% or more, may be in a range of from 60 mass % to 100 mass %, may be ina range of from 70 mass % to 100 mass %, or may be 100 mass %.

As the method for forming the solid electrolyte layer, examples include,but are not limited to, a method for forming the solid electrolyte layerby pressing the powder of the solid electrolyte material containing thesolid electrolyte and, as needed, other components. In the case ofpressing the powder of the solid electrolyte material, generally, apress pressure of about 1 MPa or more and about 400 MPa or less isapplied.

The binder used in the solid electrolyte layer may be the same as thebinder used in the above-described cathode layer.

The thickness of the solid electrolyte layer is generally about 0.1 μmor more and about 1 mm or less.

As needed, the all-solid-state battery comprises an outer casing forhousing the cathode, the anode and the solid electrolyte layer.

The form of the outer casing is not particularly limited. As the form,examples include, but are not limited to, a laminate form.

The material for the outer casing is not particularly limited, as longas it is stable in electrolytes. As the material, examples include, butare not limited to, resins such as polypropylene, polyethylene andacrylic resins.

As the all-solid-state battery, examples include, but are not limitedto, a lithium ion battery, a sodium battery, a magnesium battery and acalcium battery. The all-solid-state battery may be a lithium ionbattery.

As the form of the all-solid-state battery, examples include, but arenot limited to, a coin form, a laminate form, a cylindrical form and asquare form.

EXAMPLES Comparative Example 1

The following experiment was carried out in a glove box under an Ar gasatmosphere at a dew point of −70° C. or less, unless otherwise stated.

As starting materials, lithium sulfide (Li₂S, manufactured by MitsuwaChemicals Co., Ltd.), diphosphorus pentasulfide (P₂S₅, manufactured byAldrich), lithium iodide (LiI, manufactured by Aldrich) and lithiumbromide (LiBr, manufactured by Aldrich) were used.

The raw materials were weighed out according to the followingcomposition formula: 10Li_(1.15)LiBr·75(0.75Li₂S·0.25P₂S₅ (mol %). Then,the raw materials were mixed to obtain a mixture.

Next, 1 g of the mixture and 500 ZrO₂ balls (diameter 4 mm) were put ina ZrO₂ container (45 mL). Then, the container was hermetically closed.

The container was installed in a planetary ball mill (product name: P-7,manufactured by: Fritsch) and subjected to mechanical milling at a platerotational frequency of 510 rpm for 45 hours, thereby obtaining asulfide glass.

Under an Ar gas atmosphere, the sulfide glass was heated at a highertemperature (200° C. to 350° C.) than the crystallization temperature(Tc) of the sulfide glass measured by thermal analysis measurement,thereby obtaining a glass ceramic. The composition of the thus-obtainedglass ceramic was 10LiI·15LiBr·75(0.75Li₂S·0.25P₂S₅) on a molar basis.

The thus-obtained glass ceramic was deemed as the sulfide-based solidelectrolyte of Comparative Example 1. The BET specific surface area andcrystallinity of the thus-obtained sulfide-based solid electrolyte weremeasured. The results are shown in Table 1.

Example 1

A grass ceramic was obtained in the same manner as ComparativeExample 1. The glass ceramic was immersed in butyl butyrate for one hourfor elution and removal of impurities, glass components and unreactedraw materials, thereby obtaining a sulfide-based solid electrolyte. TheBET specific surface area and crystallinity of the thus-obtainedsulfide-based solid electrolyte were measured. The results are shown inTable 1.

Example 2

A glass ceramic was obtained in the same manner as ComparativeExample 1. The glass ceramic was immersed in butyl butyrate for 54hours, thereby obtaining a sulfide-based solid electrolyte. The BETspecific surface area and crystallinity of the thus-obtainedsulfide-based solid electrolyte were measured. The results are shown inTable 1.

Example 3

A glass ceramic was obtained in the same manner as ComparativeExample 1. The glass ceramic was immersed in butyl butyrate for 100hours, thereby obtaining a sulfide-based solid electrolyte. The BETspecific surface area and crystallinity of the thus-obtainedsulfide-based solid electrolyte were measured. The results are shown inTable 1.

Comparative Example 2

A glass ceramic was obtained in the same manner as ComparativeExample 1. The glass ceramic was immersed in butyl butyrate for 200hours, thereby obtaining a sulfide-based solid electrolyte. The BETspecific surface area and crystallinity of the thus-obtainedsulfide-based solid electrolyte were measured. The results are shown inTable 1.

Comparative Example 3

A glass ceramic was obtained in the same manner as ComparativeExample 1. The glass ceramic was immerse in butyl butyrate for 1000hours, thereby obtaining a sulfide-based solid electrolyte. The BETspecific surface area and crystallinity of the thus-obtainedsulfide-based solid electrolyte were measured. The results are shown inTable 1.

(Li ion Conductivity Measurement)

For each of the sulfide-based solid electrolytes produced in Examples 1to 3 and Comparative Examples 1 to 3, the Li ion conductivity wasmeasured by the following method. The results are shown in Table 1.

First, the sulfide-based solid electrolyte was cold-pressed at apressure of 4 ton/cm², thereby producing pellets having a diameter of11.29 mm and a thickness of about 500 μm.

Next, the pellets were placed in a container under an inert atmospherefilled with Ar gas. Then, the Li ion conductivity of the pellets wasmeasured.

For the Li ion conductivity measurement, an impedance/gain-phaseanalyzer SI1260 (manufactured by Solartron Analytical) was used.

[Production of All-Solid-State Battery]

The sulfide-based solid electrolyte produced in Example 1,LiNi_(3/5)Co_(1/5)Mn_(1/2) (NCM) as a cathode active material, and VGCF(trade name, manufactured by Showa Denko K. K.) as an electroconductivematerial, were mixed to produce a material for cathode.

In a material for anode, silicon was used as an anode active material.

In a material for solid electrolyte layer, the glass ceramic produced inComparative Example 1 was used as a solid electrolyte.

The material for cathode, the material for solid electrolyte layer, andthe material for anode were stacked in this order and pressed, therebyproducing an all-solid-state battery in which a cathode layer, a solidelectrolyte layer and an anode layer were disposed in this order.

The thus-obtained all-solid-state battery was charged. Then, the cathodelayer, which was in the form of pellets, was taken out from the chargedall-solid-state battery. The heat generation amount of the cathode layerwas measured by use of a differential scanning calorimeter (DSC). Theresult is shown in Table 1.

All-solid-state batteries were produced in the same manner as above,using the sulfide-based solid electrolytes of Examples 2 and 3 andComparative Examples 1 to 3. For each all-solid-state battery, the heatgeneration amount of the cathode layer was measured in the same manneras above. The results are shown in Table 1.

TABLE 1 Li ion Heat Immersing BET specific conduc- Crystal- generationtime surface area tivity linity amount (hr) (m²/g) (mS/cm) (%) (W/g)Comparative 0 6.7 4.5 65 1059 Example 1 Example 1 1 12.7 3.9 69 753Example 2 54 21.5 3.5 70 598 Example 3 100 33.4 2.7 75 477 Comparative200 39.2 1.2 79 316 Example 2 Comparative 1000 43.2 0.9 80 287 Example 3

As shown in Table 1, it was revealed that by the immersing, both anincrease in specific surface area and an increase in crystallinity areachieved at the same time.

Also, it was proved that as long as the immersing time is in a range offrom 1 hour to 100 hours or the BET specific surface area is in a rangeof from 12.7 m²/g to 33.4 m²/g, the sulfide-based solid electrolyteobtains a balance between the lithium ion conductivity of thesulfide-based solid electrolyte and the heat generation amount of thecathode layer containing the sulfide-based solid electrolyte.

REFERENCE SIGNS LIST

-   11. Solid electrolyte layer-   12. Cathode layer-   13. Anode layer-   14. Cathode current collector-   15. Anode current collector-   16. Cathode-   17. Anode-   100. All-solid-state battery

1. A method for producing a sulfide-based solid electrolyte comprising asulfide glass-based material that contains at least one lithium halidecompound selected from the group consisting of LiI, LiBr and LiCl, themethod comprising immersing the sulfide glass-based material, which isat least one sulfide glass-based material selected from the groupconsisting of a sulfide glass and a glass ceramic, in an organic solventhaving a solubility parameter of 7.0 or more and 8.8 or less, for 1 hourto 100 hours, thereby forming the sulfide glass-based material into aporous sulfide glass-based material, wherein the organic solvent is atleast one selected from the group consisting of butyl butyrate, diethylether, cyclohexane, toluene, chlorotoluene, hexyl acetate, n-pentane,and n-octane.
 2. The method for producing the sulfide-based solidelectrolyte according to claim 1, wherein the organic solvent is butylbutyrate.
 3. The method for producing the sulfide-based solidelectrolyte according to claim 1, wherein, when the sulfide glass-basedmaterial is a sulfide glass, the method further comprises heating thesulfide glass at a temperature higher than a crystallization temperature(Tc) of the sulfide glass, which is a temperature observed by thermalanalysis measurement, thereby obtaining a glass ceramic.
 4. A method forproducing an all-solid-state battery comprising a cathode layer thatcontains the sulfide-based solid electrolyte obtained by the productionmethod defined by claim
 1. 5. A sulfide glass-based material thatcontains at least one lithium halide compound selected from the groupconsisting of LiI, LiBr and LiCl, wherein a specific surface area of thesulfide-based solid electrolyte measured by the BET method, is from 10m²/g to 35 m²/g.
 6. The method for producing the sulfide-based solidelectrolyte according to claim 1, wherein a specific surface area of theporous sulfide glass-based material measured by the BET method, is from10 m2/g to 35 m2/g.